Recently, as a new memory device, a nonvolatile semiconductor memory device called ReRAM (Resistance Random Access Memory) is noted. The ReRAM uses a resistance memory element which has a plurality of resistance states of different resistance values, which are changed by electric stimulations applied from the outside and whose high resistance state and low resistance state are corresponded to, e.g., information “0” and “1” to be used as a memory element. The ReRAM highly potentially has high speed, large capacities, low electric power consumption, etc. and is considered prospective.
The resistance memory element has a resistance memory material whose resistance states are changed by the application of voltages sandwiched between a pair of electrodes. As the typical resistance memory material, oxide materials containing transition metals are known.
The following are examples of related art of the present invention: M. Fujimoto et al., “High-speed resistive switching of TiO2/TiN nano-crystalline thin film”, Japanese Journal of Applied Physics, Vol. 45, No. 11, 2006, pp. L310-L312; C. Yoshida et al., “High speed resistive switching in Pt/TiO2/TiN resistor for multiple-valued memory device”, Extended Abstracts of the 2006 International Conference on Solid State Devices and Materials, 2006, pp. 580-581; and K. Kinoshita et al., Applied Physics Letters, Vol. 89, 2006, 103509.
The write operation of the resistance memory element, which changes the resistance state includes the operation which changes the high resistance state into the low resistance state (set operation) and the operation which changes the low resistance state into the high resistance state (reset operation). The write operation also includes the bipolar operation which makes the set operation and the reset operation by applying voltages of different polarities and the unipolar operation which makes the set operation and the reset operation by applying voltages of the same polarity.
Generally, the switching speed of the resistance memory element making the bipolar operation is about tens nsec—hundreds nsec for both the set operation and the reset operation. The switching speed of the resistance memory element making the unipolar operation is about tens nsec for the set operation and about some μsec for the reset operation.
Thus, the switching speed of the conventional resistance memory element cannot be said to be sufficiently high in comparison with that of the other semiconductor memory devices and is required to be further increased. For the lower electric power consumption, it is preferable that the switching current is as small as possible.
According to one aspect of an embodiment, there is provided a resistance memory element which memorizes a high resistance state and a low resistance state and is switched between the high resistance state and the low resistance state by an application of a voltage, including a first electrode layer of a titanium nitride film, a resistance memory layer formed on the first electrode layer and formed of a titanium oxide having a crystal structure of rutile phase, and the second electrode layer formed on the resistance memory layer.
According to another aspect of an embodiment, there is provided a method of manufacturing a resistance memory element including forming a first electrode layer of a titanium nitride film, thermally oxidizing a surface of the titanium nitride film to form a resistance memory layer of a titanium oxide having a crystal structure of rutile phase, and forming a second electrode layer on the resistance memory layer.
According to further another aspect of an embodiment, there is provided a semiconductor memory device including a resistance memory element including a first electrode layer of a titanium nitride film, a resistance memory layer formed on the first electrode layer and formed of titanium oxide having a crystal structure of rutile phase, and a second electrode layer formed on the resistance memory layer, for memorizing a high resistance state and a low resistance state and being switched between the high resistance state and the low resistance state by an application of a voltage, and a select transistor connected to the first electrode layer or the second electrode layer of the resistance memory element.
The object and advantages of the embodiment will be realized and attained by means of the elements and combinations particularly pointed out in the claims.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the embodiments, as claimed.